I think a squirrel would be a good starting point. I also used a WASCO kit for my first few. The kits are a bit pricey until you can buy stuff in bulk such as clay, preservative and such. But for starting out they give you what you need.
Squirrels are easy to obtain and have a very tough skin for skinning. If you mess one up its easy to get another.
Skinning the toes are very tricky. My first few I'd only skin to the toes which resulted in shrunken toes. Little by little I'd skin them to the last joint. It takes practice.
Deer heads I feel are a bit easier but it is sometimes hard to get practice deer when you will make mistakes starting out. Then you end up with a bunch of small bucks everywhere and have to listen to the wife complain.
Its just easier to get another squirrel if you happen to mess something up.
I would reccomend the John Rinehart Tanning Solution as opposed to the dry preservative they give you in the kits. Its easy to use and I feel it is better. Or you could send out the cape. But it will shrink a bit and you will need to remeasure.
I found that using the JRTS resulted in less shrinking of the cape and my measurements were more accurate.
I'm no pro. I just started messing around with it a couple years ago, so I know where you are coming from.
I've done several squirrels, a few pheasants and several deer.
The pheasants weren't too bad to do. skinning was a little tricky though.
Go ahead and try your hand at it. You'll learn more with each mount.